Computer Modeling of Electronic Circuits with LTSPICE

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Computer Modeling of Electronic Circuits with LTSPICE
PHYS3360/AEP3630 Lecture 20/21

Simulation Program with Integrated Circuit Emphasis
• Originally developed at EE Berkeley • Uses mathematical models to describe circuit elements • SPICE3 is the latest variant.
- It allows DC and time transient analysis of nonlinear circuits (transistors, diodes, capacitors, etc., also digital circuitry)
- Command line driven interface - Available in public domain (written in C) - Has become de-facto the industry standard - Many spin-offs exist (use modified SPICE2 or SPICE3 as their
engine), such as HSPICE, PSPICE, WinSPICE (commercial)

SPICE Netlist – text file containing circuit description

Netlist (closer look)

* Demo of a simple AC circ.

Circuit description

v1 1 0 ac 12 sin ; v1 is an AC source of 12V amp.

r1 1 2 30 ; r1 is 30 Ohm between nodes 1 and 2

c1 2 0 100u ; c1 is 100uF between nodes 2 and 0

.ac lin 1 60 60 ; directive to perform AC analysis

.print ac v(2) ; print out the voltage from node 2

.end ; anything after .end will be ignored

SPICE directives

Commands starting with dot (.ac, .end, etc.) are known as SPICE directives


LTspice IV
• A freeware circuit simulator (Windows or *nix/Wine) • Netlist syntax is powerful but hard to visualize • LTspice has schematic capture and is much easier to
use than traditional text-based SPICE. The user can enter a circuit to be simulated via a graphical user interface • Has virtual scope, makes Bode plots, performs FFT, etc. • Worth learning about
– It is fast, expandable, powerful, and free – Most widely used noncommercial CAD electronics software

• To begin drawing the circuit, click New Schematic, or Ctrl+N • Enable grid if not shown by clicking Ctrl+G

ground (required)


• To add a component, click on the corresponding icon

• Component button contains slew of predefined components:

voltage and current sources; transistors; opamps; gates; user-defined


• You can Delete (F5 or Ctrl-X) and Move (F7) components, as well

as Drag (F8) them (keep the wires connected)


To rotate the component prior to placing press Ctrl-R

To mirror the component prior to placing press Ctrl-E

Place Diode Place Inductor Place Capacitor Place Resistor Label Node Place Ground Draw Wire

Toolbar Summary
Place Circuit Element

Simulate Zoom In Pan
Zoom Out Auto Scale Delete


Find Paste

Move Drag Undo
Redo Rotate
Mirror Place Comment
Place SPICE Directive

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Computer Modeling of Electronic Circuits with LTSPICE